1. Field of the Invention
The invention relates to an interface between a central processing unit (CPU) e.g., microprocessor and one or more coprocessors. In particular, the invention relates to a method and apparatus for allowing the execution of special purpose functions by a coprocessor which rapidly assumes control of the processor busses and is conditioned to be immediately available to perform the special purpose function.
2. Description of the Prior Art
Existing computer instruction sets are often inadequate for specific purposes. An instruction set may only need the addition of a few instructions to significantly enhance the processing capability for a particular application. One way to increase the instruction set is to redesign the central processing unit (CPU) which would be very costly and time consuming. Another more practical approach has been to add a coprocessor which extends the instruction set. In such an arrangement, the critical link is the interface between the CPU and the coprocessor. Many interfaces have been designed but they are limited in their capabilities because they cannot manipulate memory and require transfer of data between the CPU and coprocessor to provide operands for execution. Both of these operations require time. In the first instance time is lost in controlling memory through the CPU which is not involved in performing the specific instruction. In the second instance time is required to set up the coprocessor prior to execution of the function.